The present invention relates to intercom apparatus particularly adapted for use in light aircraft. More specifically, the present invention relates to a voice activated intercom enabling hands-free intra-cabin communications between pilot, co-pilot, and passengers including means for interfacing existing aircraft communications and navigation equipment (avionics) and optional stereophonic entertainment sources such an as FM tuner or cassette recorder or the like. In particular, the present intercom incorporates multi-VOX (voice or radio enabled audio) for maximizing voice intelligibility and for activating the partial-mute audio prioritizing circuitry of the present invention. In addition, the partial-mute of the present invention reduces the stereo source volume upon VOX actuation enhancing voice intelligibility without distracting interruption of the stereo audio source.
It is well known that the light aircraft cabin environment is characterized by high engine and slip-stream noise levels which, in turn, contribute to pilot (and passenger) fatigue and, more significantly, severely limit normal intra-cabin conversation, particularly between front and rear seat passengers. In addition, these high noise levels compromise the intelligibility of aircraft radio communications and so detract from the quality of stereo music to render listening unpleasant and impractical. The use of noise cancelling headsets to attenuate these inherent noises greatly reduces pilot fatigue and, where connected to conventional aircraft avionics equipment, improves the radio communications intelligibility. Such headsets are well known to the art. Where multiple users must be accommodated, however, such headsets are commonly interfaced with an intercom system which functions, in part, to electronically interconnect the various headsets and aircraft avionics. The use of aircraft intercoms is also well known to the art. The present invention, therefore, pertains to an improved aircraft intercom system adapted to maximize the users voice intelligibility and to provide an optimum integration between the multiple intercom audio sources, taking into consideration the changing communications requirements occasioned by the ever differing flight conditions.
A principal objective and advantage of any aircraft intercom system is the reduction in aircraft noise and the corresponding improvement in voice or radio intelligibility afforded by the noise cancelling headphones generally used in conjunction with the intercom system. As previously discussed, modern aircraft headsets block substantially all aircraft noise allowing the user to easily understand voice conversation and to appreciate locally generated music, where provided.
Unfortunately, the microphones associates with the various passengers' headsets represent significant potential sources of noise since they are of necessity positioned within the noisey aircraft cabin. Several known aircraft intercom systems have addressed this problem by incorporating voice actuated circuitry (VOX) to simultaneously enable the several headset microphones, but only when voice audio is detected from any one of the microphones. This prior art arrangement has proved somewhat satisfactory at least to the extent that noise entering these microphones is not amplified nor transferred to the occupants' headsets until one of the users speaks. In this manner the fatigue level is substantially reduced as virtually no noise is present in the headsets during periods of non-conversation. However, when any one of the occupants speaks, substantial noise is present due to the summation of aircraft noise contributed by the plurality of simultaneously enabled headsets.
Therefore, this solution, which reduces fatigue caused by the constant drone of the aircraft, does little to enhance the voice intelligibility of any given cabin occupant. The noise, switched `off` during lulls in conversation, is again present in the headsets whenever an occupant speaks. More specifically, conventional aircraft intercoms interconnect all passenger (or crew) microphones to a common VOX arrangement which functions to enable all such microphones upon the detection of legitimate voice audio from any one microphone. Due to the nature of these prior art VOX circuits, `information` identifying which passenger, at any given instant, is speaking is lost and, therefore, the single output from these prior art VOX circuits must necessarily and simultaneously enable all microphones. It will be appreciated that enabling all aircraft microphones, where only one is in use, causes additional noise from the `inactive` microphones to be needlessly added to the voice signal thereby reducing the signal-to-noise ratio and the corresponding intelligibility of the desired voice signal. For example, in a system used by four occupants, noise from all four microphones is added to the voice audio signal from the one active microphone. One voice signal--four noise `signals`.
The present invention, by contrast, utilizes a multi-VOX arrangement wherein `information` identifying which microphone(s) is active selectively enables only that microphone(s). Thus, in the above example, only one `noise` signal, rather than four, is added to any given voice signal. In this manner the voice signal-to-noise ratio and intelligibility are significantly improved over conventional intercom systems.
It has also been found that music is quite pleasurable in light aircraft where, as described above, proper noise cancelling headsets are employed. Music is conventionally accommodated by interfacing a stereo FM tuner or cassette tape player with an aircraft intercom. In addition, it is generally desirable to interface the aircraft avionics equipment into the intercom to permit the pilot to communicate with, or monitor, the various aviation frequencies as required for the safe conduct of the flight. Thus, as many as three or more disparate audio sources may be operatively connected through the intercom at any given time. It will, therefore, be appreciated that a proper `mix` or integration between these various intercom inputs is required in order that each of these audio input sources may be utilized to the maximum potential. As will be described in more detail below, the present invention provides a truly unique and functional interplay between the intracabin intercom, air-to-ground communications, and music sources wherein each attains a high degree of utility approaching that which would obtain were the given source the only source.
Intercoms known to the art have never achieved a very satisfactory or high level of input source integration. Severe source integration limitations, characteristic of prior art intercoms, often restrict the use of these intercoms to one `function` at a time or, alternatively, segregate the various aircraft occupants into groups, each group utilizing the intercom system only in its partial capacity. For example, it has long been recognized that music can interfere with important air-to-ground communications and, consequently, one known prior art approach restricts music listening to the passengers and, similarly, the radio communications to the pilots. This, of course, is highly unsatisfactory since many passengers enjoy listening and following the progress of the flight by monitoring the air-to-ground communications and feel more a part of the flight when privy to such communications. At least as important, this solution is entirely unsatisfactory since it precludes the pilot from the highly enjoyable music feature of the intercom system.
Recognizing that segregation of aircraft occupants is highly unsatisfactory, other known systems have adopted a music muting arrangement whereby audio from either the communications radio or a passenger's microphone totally `mute` the music. Although this arrangement assures maximum voice intelligibility, the repeated and nearly constant interruption or `punctuation` of the music occasioned by routine radio communications, particuarly when monitoring a busy ATC frequency or unicom channel, or by `idle` cabin chatter has been found to be unduly distracting and annoying to the extent that passengers refuse to talk while the music is playing. In addition, the annoyance of repeated interruptions during an IFR flight usually requires that the music simply be turned-off.
The present invention, by contrast, incorporates a partial mute arrangement whereby the level or volume of the music is significantly, but not totally, reduced whenever an intercom microphone or communications radio audio signal is present. It has been found that reducing the level of music affords a high degree of voice audio intelligibility without the obnoxious interruptions common to prior art total mute systems. In fact, experiments demonstrate that a relatively large reduction in volume can be implemented with only a barely perceptible loss of music listening pleasure. Therefore, it will be appreciated that the partial mute of the present invention permits all occupants of the aircraft, including the pilot, to enjoy the full benefit of airborne music even when monitoring crowded ATC frequencies or engaging in protracted intra-cabin conversations.
Another difficulty with known intercom systems is audio source interference arising between regular intra-cabin intercom usage and aircraft radio reception. It is, simply, difficult, if not impossible, to listen to and comprehend two voices at the same time. In addition to this obvious loss of intelligibility, the continuing presence of a `second` voice is quite distracting to the intercom users. Known prior art systems have wholly failed to address this significant shortcoming. Use of such systems generally requires that the aircraft radios be turned-down during flight or, where radio communications is necessary for instrument flight (IFR) or the like, that normal intra-cabin conversations be discontinued or, at the least, frequently interrupted by the continuous flow of radio transmissions. This, of course, discourages the monitoring of ATC, flight watch, or unicom frequencies during visual (VFR) flight and, importantly, severly restricts the utility of the intercom for normal intra-cabin conversation during IFR flight.
The present invention solves this source integration problem by combining the features of partial muting, discussed above, with pilot selectable intercom/aircraft radio priority. In arriving at the present arrangement, it was first recognized that changing flight conditions necessarily alter the relative importance of the respective audio source inputs. Thus, for example, on a clear day, the flight might be conducted with only marginal interest and attention given to the aircraft radio while, on an instrument flight in bad weather, aircraft radio communication is paramount in importance. But notwithstanding the relative importances assigned to the various intercom inputs during a given flight, or flight segment, it remains highly desirable and necessary to accommodate the relatively lesser importance inputs. Thus, during a VFR flight where intra-cabin conversation will likely be given priority over the aircraft communications radio, monitoring of certain radio channels such as flight-watch and unicom is highly desirable--so long as such monitoring can be effectuated without obnoxious interruption to intra-cabin use of the intercom. During instrument flight conditions, by contrast, the communications radios may well be given priority but, again, it remains desirable to accommodate normal intra-cabin intercom usage. The present invention accomplishes these objectives. First, it permits the pilot to select the input to be given `higher` priority during any given flight segment. Second, an audio signal from the non-selected input is assured. The use of the present partial mute feature, discussed above with respect to the stereo input source, is essential to the extent that total muting of the non-selected input does not permit the occupants to `keep-tabs` on the activities of such non-selected source. In short, the partial mute feature places the non-selected audio `in the background` whenever the prioritized input is active. This has been found to facilitate the monitoring of such audio source as the users can, notwithstanding the reduction in audio level, still obtain the `gist` of the activity on that input.
It is therefore an object of the present invention to provide an intercom adapted for use in light aircraft or other high noise environments. It is a further object that the intercom shall be capable of efficiently integrating several audio sources including, for example, user microphone audio, communications audio, and entertainment program audio. The intercom shall maximize audio source intelligibility by reducing environmental noise and by reducing interference between competing intercom input sources. In furtherance of these objects, each user shall be provided with a separate intercom input and, preferably, with separate voice activation circuits whereby only the microphones of those persons actually speaking at any given instant shall be enabled. Partial muting shall be provided on the entertainment input source to facilitate reduction of the level whenever user microphones or other important input sources are active. Selectable input priority shall be combined with partial muting to enable the pilot to choose the input to be assigned the highest priority and to automatically lower the audio signal level of those non-selected inputs.